He gave an exit interview to the Sydney Morning Herald, explaining the switch. Long story short, Google is too big a company now, and Facebook can offer him more money, presumably through its IPO down the road.

"The energy [at Facebook] is just amazing, whereas it can be very challenging to be working in a company the size of Google."

He also says, he received a "compelling personal pitch" from Mark Zuckerberg himself.

Of course, it doesn't hurt that Facebook's offer was "much more compelling both financially and in terms of the work there".

On Google pulling the plug on Wave: "It wasn't something that I would like to bet my life on, but all that excitement we created when we first unveiled the project was based on something real. It takes a while for something new and different to find its footing and I think Google was just not patient...It's not my intention or Facebook's intention that I will go on to do something similar [to Wave.]"

On the Social Network: "It came out literally as I was talking to Mark and some of the people who were working there. I decided that Hollywood shouldn't have quite that impact on my professional choices and so I decided not to see it."